This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. What is the function of the novel class-I-like protein, MR1, in regulating mucosal immunity? MR1 is highly conserved MHC-I-like protein in mammals, that activates a unique population of T cells with an invariant T cell receptor. Interestingly the development of these MR1 activated T cells is dependent upon the commensal flora of the gut. Our experiments are using biochemical, cellular, transgenic and crystallographic approaches to determine the structure and function of MR1 proteins. MS is one of the approaches that represents a cross-campus and cross-resource collaboration.